Method for layout design and structure with inter-layer vias

ABSTRACT

A computer implemented layout method for an integrated circuit (IC) structure and IC structure are provided. The layout method can include placing a circuit cell and an inter-layer via together in a first device layer of the IC structure, and placing a metal pattern in a second device layer of the IC structure. The inter-layer via and the metal pattern may be configured to form a direct connection channel for the circuit cell and the metal pattern.

BACKGROUND

Integrated circuit (IC) structures and design have experiencedcontinuous and rapid improvement with the increase in manufacturingcapabilities and reduction in chip size. Improvements in integrationdensity may be attributed to repeated reduction in minimum feature sizewhich allows for more components to be integrated into a given chiparea. Improvements in planar processing and integrated circuits formedby planar processing are challenged by physical limitations posed bydensity complexity of reduction in size.

Large scale integrated circuit (IC) chips include many circuit elements.IC design often requires considerable effort for placement of cells.Place and route programs are often used to create IC chip layouts. Someplacement tools cannot handle cell placement well. IC chips requirerouting overheads to connect different portions of the IC chip.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a monolithic three dimensional (3D) IC structure inaccordance with some embodiments.

FIG. 2 is a layout view of a circuit cell bundled with inter-layer viasin accordance with some embodiments.

FIG. 3 is another view of the monolithic 3D IC structure of FIG. 1according to an embodiment.

FIG. 4 is a flow-chart illustrating a computer implemented layout methodfor placing circuit cells with bundled inter-layer vias in accordancewith some embodiments.

FIG. 5 is a flow-chart illustrating a computer implemented layout methodfor designing power supply network in a monolithic 3D IC chip inaccordance with some embodiments.

FIG. 6 is a flow-chart illustrating a computer implemented layout methodfor designing a monolithic 3D IC in accordance with some embodiments.

FIG. 7 is a block diagram illustrating an exemplary computing systemsuitable for implementing embodiments of the present disclosure.

DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are merely examples andare not intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

One aspect of the disclosure relates to three dimensional (3D) ICstructures and chips. In an embodiment, structural elements andconfigurations are provided for monolithic three dimensional (3D) ICsand chips. Another aspect of the disclosure relates to a method forlayout design, such as a design method for connecting circuit cells indifferent device layers. Various embodiments of the present disclosurewill be described hereinafter with reference to the attached drawings.

FIG. 1 illustrates a monolithic three dimensional (3D) IC structure 100in accordance with various embodiments. The monolithic 3D IC structure100 includes a device layer 102 and a device layer 112. Device layer 102includes a circuit cell 104. In an embodiment, circuit cell 104 isplaced in the device layer 102. According to another embodiment, circuitcell 104 and an inter-layer via 125 are bundled, as shown in FIG. 1. Insome embodiments, bundling circuit cell 104 and inter-layer via 125refers to treating circuit cell 104 and inter-layer via 125 as if theywere an integral unit during a placement stage. In some embodiments,bundling circuit cell 104 and inter-layer via 125 refers to including apredetermined location for connecting inter-layer via 125 within a cellboundary of circuit cell 104. In an embodiment, bundling includesplacing the circuit cell 104 and a portion of inter-layer via 125 indevice layer 102 in close proximity to and/or coupled with a particularlocation, such as a location 106. In another embodiment, bundlingincludes configuring the circuit structure of the circuit cell 104 andinter-layer via 125 to provide a direct connection between circuit cell104 and a different layer, such as device layer 112. In an embodiment,the direct connection provided by inter-layer via 125 is usable to carrya supply power voltage, an analog signal, or a logic signal.

In an embodiment, inter-layer vias, such as inter-layer via 125, connectcircuit elements in the device layer 102 with circuit elements in thedevice layer 112. In some embodiments, by using inter-layer via 125,power supply metal lines, such as a metal pattern 217 or a metal pattern237 in FIG. 2, become shorter and/or fewer due to the direct connectionbetween layers 102 and 112. In comparison to routing connections to theouter perimeter of a layer, inter-layer vias, such as inter-layer via125, can provide shorter connections for monolithic 3D IC 100. In anembodiment, inter-layer vias, such as inter-layer via 125, allow forshorter connections within monolithic 3D IC 100 which results in powerconsumption reduction of the monolithic 3D IC 100 and lowered routingoverheads. By way of example, inter-layer via 125 provides a shorterpath between layers 102 and 112 compared to running a connection to theedge of a layer for routing along the side of 3D IC 100. Thus, in someembodiments, bundling an inter-layer via, such as inter-layer via 125,with a circuit cell reduces the amount of power supply routing and easesrouting overheads by reducing the amount of routing in the 3D IC 100.

In some embodiments, inter-layer vias, such as inter-layer via 125, havea small feature size, such as a footprint of 0.05 μm×0.05 μm. In someembodiments, circuit cells have a footprint of 0.54 μm×0.48 μm. Byproviding a small feature size, inter-layer via 125 provides greaterdensity and flexibility in designing a monolithic 3D IC structure.Inter-layer via 125 provides greater flexibility by allowing for moreplacement locations due to the small feature size. In comparison,through-silicon-vias of other approaches have a typical feature size of6 μm×6 μm.

Inter-layer via 125 as shown in FIG. 1 is illustrated as a verticalstructure. In an embodiment, inter-layer via 125 is vertical, orsubstantially vertical to connect layers 102 and 112. In someembodiments, inter-layer via 125 is vertically straight, orsubstantially vertical to connect layers 102 and 112. In anotherembodiment, the inter-layer vias, such as inter-layer via 125, vary inshape to allow for a slanted or offset vertical connection, and includemultiple layers of materials and landing structures.

In an embodiment, the device layer 102 and device layer 112 havedifferent power supply voltages. Circuit cell 104 is configured toreceive power, such as a power supply line voltage (e.g., VDD). Anexemplary power supply line voltage (VDD) received by circuit cell 104is 3.3 volts (V). In other embodiments, voltage level shifter 108 ofcircuit cell 104 is configured to provide a multilevel supply power,such as one or more of a high supply voltage (e.g., VDDH) and low supplyvoltage (e.g., VDDL). In an embodiment, a voltage level shifter 108 isprovided to facilitate both signal communication and power distribution.For instance, the device layer 102 may have a 3.3 V high voltage powersupply (VDD) which is supplied from outside the monolithic 3D IC chip100. The device layer 112 may have a 1.2 V high supply voltage (VDDH)which is supplied from the device layer 102. In an embodiment, thecircuit cell 104 uses the voltage level shifter 108 to convert a 3.3Vpower input to a 1.2V power output to be supplied to the device layer112 through the inter-layer vias 125. In some embodiments, in additionto a power connection, inter-layer vias, such as inter-layer via 125,also include signal or control connections, the voltage of which is alsoconverted by a voltage level shifter, such as voltage level shifter 108.

In an embodiment, monolithic 3D IC 100 is an integrated circuitstructure that contains active and passive devices (e.g., transistors,diodes, resistors, capacitors, etc.) that are made in and on the surfaceof a semiconductor material, such as a silicon (Si) wafer. In anembodiment, monolithic 3D IC 100 includes a single block or monolithicstructure interconnected to an insulating layer over the structure, andone or more device layers, such as device layer 102, to produce a solidintegral monolithic-IC. In an embodiment, devices (e.g., transistors,diodes, resistors and capacitors) of monolithic 3D IC 100 are fabricatedon the same single chip of a single silicon crystal to include isolatedp-n junctions, and interconnections adjacent to insulator layers orregions of device layers 102 and 112 without shorting adjacent areas.The inter-layer via 125 is an example of an interconnection between oneor more device layers.

As shown in FIG. 1, the device layers, such as device layer 102 anddevice layer 112, are formed based on a monolithic semiconductor body inthe monolithic 3D IC 100. The device layer 102 and device layer 112 eachinclude active elements, in some embodiments. By way of example, activeelements include logic circuitry and/or memory circuitry. According toan embodiment, inter-layer vias, such as the inter-layer via 125, areplaced anywhere within the area of any circuit level.

During a layout process, inter-layer via 125 may be bundled, or placedtogether, with the circuit cell 104. In an embodiment, a place and routecomputer program places inter-layer via 125 and circuit cell 104together. In an embodiment, placing a circuit cell, such as circuit cell104, includes designing the position/location of the circuit cell in adevice layer, such as device layer 102. During manufacturing of the 3DIC 100, inter-layer vias, such as inter-layer via 125 may be formedaccording to the layout to directly connect circuits of device layer 102at location 106 to elements at a location 116 in the device layer 112.

FIG. 2 is a layout view of the circuit cell 104 bundled with aninter-layer via according to an embodiment. The circuit cell 104includes the voltage level shifter 108, a plurality of metal patterns212, 214, 217, 222, 225, 237 and 242, and a plurality of inter-layervias 223, 226, 238 and 243. In an embodiment, inter-layer vias 223, 226,238 and 243 are connections similar to the inter-layer via 125 ofFIG. 1. In an exemplary embodiment, inter-layer vias 223, 226, 238 and243 each include one or more metal layers and via material toelectrically connect device layer 102 and device layer 112. In anotherembodiment, inter-layer vias 223, 226, 238 and 243 are each aninter-layer via like the inter-layer via 125 of FIG. 1. The metalpatterns 222, 225, 237 and 242 overlay the inter-layer vias 223, 226,238 and 243, respectively.

In an embodiment, the metal patterns 212 and 214 are exemplary groundlines (GND). The metal pattern 217 receives power supply line voltage(VDD), such as 3.3V, in some embodiments. The metal pattern 237 is anexemplary supply line to provide voltage converted by voltage levelshifter 108. In an embodiment, voltage level shifter 108 of circuit cell104 is configured to provide a multilevel supply power, such as one ormore of a high supply voltage (e.g., VDDH) and low supply voltage (e.g.,VDDL), to metal pattern 237. In an exemplary embodiment, metal pattern237 supplies high supply voltage (VDDH) which is tied to VDD, or in somecases lower than the VDD. Alternatively, metal pattern 237 supplies lowsupply voltage (VDDL) which is lower than the VDDH. The voltage levelshifter 108 converts VDD from metal pattern 217 to VDDH or VDDL formetal pattern 237 for use by circuit cells of device layers 102 and 112.The metal patterns 222, 225 and 242 are exemplary input, enable andoutput signal lines, respectively. References to metal patterns, such asmetal pattern 217 and 237 may relate to power rails of the IC structureof FIG. 2. In other embodiments, circuit cell 104 is configured toprovide a multi-level supply, such as one or more of a high supplyvoltage (e.g., VDDH) and low supply voltage (e.g., VDDL).

In an embodiment, the inter-layer vias 223, 226, 238 and 243 are bundledwith the voltage level shifter 108. In an embodiment, bundling ofinter-layer vias 223, 226, 238 and 243 with the voltage level shifter108 includes placing the voltage level shifter 108 and a portion ofinter-layer vias 223, 226, 238 and 243 in device layer 102 in closeproximity to and/or coupled with a particular location, such as location106, of circuit cell 104. A place and route computer program will placethe circuit cell 104 together with inter-layer vias 125 in location 106of device layer 102. In an embodiment, four landing metal patterns, notshown in FIG. 2, for the inter-layer vias 223, 226, 238 and 243 will beplaced in a corresponding layer, such as layer 112 of FIG. 1, and inalignment with inter-layer vias 223, 226, 238 and 243 in layer 112. Inan embodiment, the landing metal patterns on two different device layersare aligned when metal patterns share a vertically overlapping area. Inan embodiment, other kinds of circuit cells, such as a logic cell, arebundled with inter-layer vias 223, 226, 238 and 243.

In an embodiment, circuit cell 104 is bundled with inter-layer vias 223,226, 238 and 243 to allow for point-to-point connection. By way ofexample, circuit cell 104 may be aligned with and/or correspond to thelocation of metal pattern 217, which is an exemplary first high voltagepower supply line (VDD), and another rail of the circuit device 104aligns with an interlayer metal pattern 237, which is an exemplarysecond high voltage power supply line (VDDL).

In FIG. 2, metal patterns 222, 225, 237 and 242 are configured to becoupled to at least one set of circuit devices between the metalpatterns 212 and 214 (GND). It should be appreciated that additionalsets of circuit devices may be included in the circuit cell 104 betweenmetal patterns 222, 225, 237 and 242.

FIG. 3 is another representation of the monolithic 3D IC structure ofFIGS. 1 and 2, in accordance with some embodiments. The monolithic 3D ICchip 300 includes circuit cell 104 placed in device layer 102, shown asan upper layer. The circuit cell 104 includes the voltage level shifter108 and the metal patterns 222, 225, 237 and 242 which connect thevoltage level shifter 108 to various other circuits (not shown) in thedevice level 102. The metal patterns 222, 225, 237 and 242 overlay theinter-layer vias 223, 226, 238 and 243, respectively. During a designprocess, a computer implemented place and route program places thevoltage level shifter 108, the metal patterns 222, 225, 237 and 242 andthe inter-layer vias 223, 226, 238 and 243 together as a bundled device.The place and route program also places corresponding metal patterns364, 367, 379 and 384, which are vertically aligned to the inter-layervias 223, 226, 238 and 243, respectively, in the lower device layer 112.The metal patterns 364, 367, 379 and 384 lead to other circuit cells(not shown in FIG. 3) in the lower device layer 112. As a result, thevoltage level shifter 108 in the device layer 102 and circuits in thelower device layer 112 are connected through the inter-layer vias 223,226, 238 and 243 and the metal patterns 222, 225, 237, 242, 364, 367,379 and 384. In some embodiments, the inter-layer vias 223, 226, 238 and243 are configured to carry a power supply voltage, an analog signal, ora logic signal. Because the inter-layer vias 223, 226, 238 and 243 arebundled with the voltage level shifter 108, power distribution for layer112 can be reduced and routing congestion of monolithic 3D IC chip 300can be reduced due to chip area not used for power distribution in layer112. In some embodiments, the inter-layer vias 223, 226, 238 and 243 areformed by a monolithic 3D IC process or by other inter-layer viaformation processes.

Referring again to FIG. 3, layer 102 may have multiple metal andinsulation layers for metal patterns 217, 222, 225, 237 and 242according to various embodiments of the present disclosure. Metalpatterns 217, 222, 225, 237 and 242 can be in different metal layers,and associated inter-layer vias 223, 226, 238 and 243 can be indifferent metal layers. Similarly, the metal patterns 364, 367, 379 and384 can be in different metal layers.

In an embodiment, the structure shown in FIG. 3 can be made into a cubecell 300, e.g., the metal patterns 364, 367, 379 and 384 in the lowerdevice layer 112 can be aligned with the circuit cell 104 that includesthe voltage level shifter 108 and inter-layer vias 223, 226, 238 and243. Instead of separately placing circuit cell 104 in layer 102 andplacing the corresponding metal patterns 364, 367, 379 and 384 inanother device layer, a place and route computer program can place thecube cell 300 in a monolithic 3D IC design in locations, such aslocation 106, to provide inter-layer connections between device layer102 and device layer 112. In an embodiment, a place and route computerprogram can perform connections within layer 102 or 112, with the cubecell 300. In an embodiment, metal patterns 364, 367, 379 and 384 in thelower device layer 112 provide power or signaling connections withinlayer 112.

FIG. 4 is a flow-chart illustrating a computer implemented layout method400 for placing circuit cell 104 with inter-layer vias, such asinter-layer via 125, according to various embodiments of the presentdisclosure. The layout method 400 includes placing circuit cells, suchas circuit cell 104. In block 410, the layout method includes placingthe circuit cell 104 of FIG. 3 in a first device layer 102. The circuitcell 104 can include voltage level shifter 108 and a bundled inter-layervia, such as inter-layer via 223 of FIG. 3. In block 420, the layoutmethod places an exemplary metal pattern 364 in a second device layer112 as shown in FIG. 3. The metal pattern 364 connects to other circuitsin the second device layer 112. In block 430, the layout method alignsthe inter-layer via 223 to correspond with the location of the metalpattern 364 and thus, to form an inter-layer connection that provides adirect connection between the circuit cell 104 in the first device layer102 and circuits in the second device layer 112.

FIG. 5 is a flow-chart illustrating a computer implemented layout method500 for placing elements in a monolithic 3D IC chip in accordance withsome embodiments. The method of FIG. 5 may be implemented by a place androute program. In block 510, the place and route program placesintra-layer power rail connections, such as metal patterns 212 and 214,in a first device layer 102. In an embodiment, intra-layer power railconnections, such as metal patterns 212 and 214, are connections withina layer 102. In block 520, the place and route program places a bundleddevice, such as circuit cell 104 bundled with inter-layer vias 223, 226,238 and 243 as shown in FIG. 3, to correspond with locations in layers102 and 112. In an embodiment, inter-layer vias 223, 226, 238 and 243may be aligned with and/or correspond to the location of metal patterns223, 226, 238 and 243 of layer 112 in locations which reduce the routingoverhead of the 3D IC chip. In block 530, the place and route programplaces connections to the inter-layer vias 223, 226, 238 and 243 to themetal patterns 364, 367, 379 and 384 in device layer 112. In anembodiment, metal patterns 364, 367, 379 and 384 are associated with oneor more power supply connections for device layer 112.

FIG. 6 is a flow-chart illustrating a computer implemented layout method600 for designing a monolithic 3D IC in accordance with someembodiments. In block 610, a place and route program places a pluralityof circuit cells, such as circuit cell 104, in two device layers, suchas layers 102 and 112, along with a cube cell, such as the cube cell 300of FIG. 3. The cube cell 300 of FIG. 3, with bundled inter-layer vias223, 226, 238 and 243, may be placed in block 610 for connecting circuitcells, such as circuit cell 104, placed in various device layers, suchas layers 102 and 112. In block 620, the place and route program routesconnections from at least one of the plurality of circuit cells, such ascircuit cell 104, of the cube cell 300 to create a monolithic 3D ICdesign. In block 630, an evaluating program is executed on themonolithic 3D IC design for checking the design against one or morepredetermined global routing rules and timing goals. Therefore, in someembodiments, the occurrence of global routing and timing violations isevaluated, and individual violates are identified. If any violation isdiscovered in block 630, the place and route program may relocate thecube cell 300 in block 640 to meet a predetermined global routing ruleand/or a predetermined timing goal. In an embodiment, a global routingrule may be provided by a chip foundry to ensure that a layout for an ICdesign can be correctly and satisfactorily manufactured. In anembodiment, one or more timing goals may be set by an IC circuitdesigner to configure different parts of the IC chip to worksynchronously and to achieve an overall speed goal. In some embodiments,blocks 630 and 640 are executed repeatedly to iteratively reduce routingcongestion and improve timing margins, as locations of circuit cell 104are determined. For example, the place and route program may relocatethe cube cell 300 in block 640 if any violation is discovered in block630, and can continue to evaluate locations for placing the cube cell300.

FIG. 7 is a block diagram illustrating an exemplary computing system 700suitable for implementing various embodiments of the present disclosure.The computing system 700 includes a server computer 702 and a pluralityof workstations 731-739 which are connected to the server computer 702through a networking link 728. The server computer 702 includes aprocessor 712, a memory 714, a storage 716 and a network interface 718which facilitates communication with the work stations 731-739.According to an embodiment of the present disclosure, the computersystem 700 performs specific operations by the processor 700 to executeone or more sequences of instructions which may be a part of a place androute program contained in the system memory 714. Instructions may beread into the system memory 714 from the storage 716. The storage 716may also be used to store a layout database generated by the place androute program. In an embodiment, hard-wired circuitry may be used inplace of, or in combination with, software instructions to implement thepresent disclosure. Thus, embodiments of the present disclosure are notlimited to any specific combination of hardware circuitry and/orsoftware.

Referring again to FIG. 7, the work stations 731-739 serve as terminalsfor the server computer 702. Users can enter commands and receivecomputational results from the computing system 700 through the workstations 731-739.

According to an embodiment, a computer implemented layout methodincludes placing a circuit cell and an inter-layer via together in afirst device layer of an integrated circuit (IC) design, and placing ametal pattern in a second device layer of the IC design. The firstinter-layer via and the metal pattern are configured to form a directconnection channel for the circuit cell and the metal pattern.

According to an embodiment, a computer implemented layout methodincludes placing a circuit cell and an inter-layer via together in afirst device layer of an integrated circuit (IC) design, and the firstdevice layer includes at least one active component. A connectionbetween the first circuit cell and a power supply rail within the firstdevice layer is placed, and a metal pattern in a second device layer ofthe IC design is placed, where the second device layer includes a secondpower supply voltage connection. The inter-layer via and the metalpattern are configured to form a direct connection channel between thefirst device layer and the second device layer

According to an embodiment, a 3D integrated circuit includes a circuitcell, a metal pattern, and an inter-layer via. The circuit cell is in afirst device layer of the 3DIC structure. The metal pattern is in asecond device layer of the 3DIC structure. The inter-layer via connectsthe circuit cell in the first device layer of the 3DIC structure at apredetermined location and connects the metal pattern in the seconddevice layer of the 3DIC structure. The predetermined location is withina cell boundary of the circuit cell in the first device layer of the3DIC structure.

The foregoing outlines features of several embodiments so that those ofordinary skill in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of an embodimentintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A computer implemented layout method, the methodcomprising: placing a circuit cell and an inter-layer via together in afirst device layer of an integrated circuit (IC) design; and placing ametal pattern in a second device layer of the IC design, wherein thefirst inter-layer via and the metal pattern are configured to form adirect connection channel for the circuit cell and the metal pattern. 2.The method of claim 1, wherein the circuit cell includes at least oneactive component.
 3. The method of claim 1, wherein the circuit cell andinter-layer via are placed in a location within the first device layerof the IC design, and wherein the location within the first device layercorresponds to a location within the second device layer.
 4. The methodof claim 3, further comprising placing a power supply line in the firstdevice layer to the circuit cell.
 5. The method of claim 3, wherein thefirst device layer is placed with a first power supply line and thesecond device layer is placed with a second power supply line.
 6. Themethod of claim 6, wherein the circuit cell includes a voltage levelshifter.
 7. The method of claim 1, wherein the inter-layer via isconfigured to carry a power supply voltage.
 8. The method of claim 1,wherein the inter-layer via is configured to carry an analog signal or alogic signal.
 9. The method of claim 1, further comprising: placing aplurality of circuits in the IC design, at least one of the plurality ofcircuits being connected to the circuit cell; evaluating routing andtiming violations of the IC design; and relocating the circuit cell andthe metal pattern to meet a predetermined routing rule and timing goal.10. The method of claim 1, wherein the IC structure is a monolithicthree dimensional IC (3DIC) structure.
 11. A computer implemented layoutmethod, the method comprising: placing a circuit cell and an inter-layervia together in a first device layer of an integrated circuit (IC)design, the first device layer including at least one active component;placing a connection between the first circuit cell and a power supplyrail within the first device layer; and placing a metal pattern in asecond device layer of the IC design, the second device layer includinga second power supply voltage connection, wherein the inter-layer viaand the metal pattern are configured to form a direct connection channelbetween the first device layer and the second device layer.
 12. Themethod of claim 11, wherein the circuit cell includes a voltage levelshifter.
 13. The method of claim 11, wherein the inter-layer via isconfigured to carry a power supply voltage.
 14. The method of claim 11,wherein the inter-layer via is configured to carry an analog or a logicsignal.
 15. The method of claim 11, further comprising: placing aplurality of circuits in the IC design, at least one of the plurality ofcircuits being connected to the circuit cell; evaluating routing andtiming violations of the IC design; and relocating the circuit cellalong with the metal pattern to meet a predetermined routing rule andtiming goal.
 16. A three dimensional integrated circuit (3DIC) structurecomprising: a circuit cell in a first device layer of the 3DICstructure; a metal pattern in a second device layer of the 3DICstructure; and an inter-layer via connecting the circuit cell in thefirst device layer of the 3DIC structure at a predetermined location andconnecting the metal pattern in the second device layer of the 3DICstructure, the predetermined location being within a cell boundary ofthe circuit cell in the first device layer of the 3DIC structure. 17.The integrated circuit of claim 16, wherein the location within thefirst device layer corresponds to a location within the second devicelayer.
 18. The integrated circuit of claim 16, wherein the circuit cellincludes a voltage level shifter.
 19. The integrated circuit of claim16, wherein the inter-layer via is configured to carry a power supplyvoltage, an analog signal, or a logic signal.
 20. The integrated circuitof claim 16, wherein the inter-layer via is vertical or substantiallyvertical to the first device layer and the second device layer.